1. Field of the Invention
This invention relates generally to rechargeable battery-powered devices and, more particularly, to devices that are adapted for direct connection to sources of charging energy.
2. Description of the Related Art
Rechargeable battery-powered devices comprise electrical loads powered by one or more secondary batteries. The secondary batteries can receive electrical energy when the voltage they supply decreases to a level at which the device is inoperable or otherwise does not function properly. The electrical energy recharges the secondary batteries so the voltage they supply returns to normal. Most rechargeable battery-powered devices are designed to mate with a holder or cradle that provides a source of recharging electrical energy. When the device is mated with the charging cradle, electrical connections are automatically made and, when the charging cradle is activated, the secondary batteries contained in the device are recharged. The secondary batteries therefore can be used multiple times without being discarded.
Battery-powered devices include an on-off switch that, when in an on condition, connects the device battery to the device electrical loads. It can be very easy to mistakenly leave a battery-powered device in an on condition when it is being recharged. If the device is mated with the charging cradle while in the on condition, the electrical energy intended for the secondary battery is diverted to electrical loads within the device. For example, many photographic cameras include a flash illumination system having a flash tube and various capacitors that are charged up to operating levels of approximately 330 volts. If a camera is placed in a charging cradle while the camera flash system is on, then much of the electrical energy intended for the secondary battery likely will be consumed by maintaining the electrical charge on the flash capacitors. As a result, the battery will not be recharged and the electrical energy might even be taken from the battery faster than the energy is stored, leaving the battery in a run-down condition. When a user removes the camera from the charging cradle, expecting that the battery will be ready for use, the user may discover that the battery does not have adequate energy to permit camera or flash operation.
It is known to provide a mechanical interlock that prevents current from being provided to the rechargeable battery-powered device if the device is mated with a charging cradle when in the on condition. This prevents the device load from taking the charging current and prevents the secondary battery from becoming run down, but does not provide recharging energy to the battery. For example, see U.S. Pat. No. 4,260,230 to Suzuki. It also is known to mechanically disconnect the device electrical load from the battery during recharging, thereby permitting the battery to be recharged even if the device is left on, but mechanical interlocks can be rather heavy and cumbersome to incorporate and also can be unreliable and relatively expensive. See, for example, U.S. Pat. No. 4,794,315 to Pederson and U.S. Pat. No. 4,947,514 to Gerke. Finally, rather complicated microprocessor-based interlock systems that disconnect the device load from the battery are known, which are even more complicated than mechanical interlocks and suffer from having great cost and complexity. See, for example, U.S. Pat. No. 5,049,802 to Mintus relating to a rechargeable electrical vehicle.
From the discussion above, it should be apparent that there is a need for a rechargeable battery-powered device that includes a relatively simple interlock that prevents the device electrical load from consuming recharge energy intended for the secondary battery when the device is placed in a charging cradle for recharging and the device is left on. The present invention satisfies this need.